An arrow that points at interesting objects in the sky, inspired by the art installation at the JPL mall.
A pointing mechanism (an arrow and/or a laser pointer) that will point out interesting targets in the sky either automatically or in response to user input.
Targets may include
- Stars, galaxies, and other interesting deep sky objects
- Earth satellites
- Locations on Earth (mountains, cities, friends)
- Airplanes?
The mechanism should have a screen to display what is being observed.
Steppers, servos, simple DC motors?
Need a motor driver
System-on-a-chip (SoC) like a Raspberry Pi or microcontroller like ESP/Arduino?
- SoC is way easier to work with (existing astronomy libraries, etc) and has no storage/RAM limitations, but boots slowly and has higher power consumption.
- Microcontroller boots instantly and has lower power usage, but is very limited (a few kBs of RAM).
USB plug and built-in battery? Need a charge controller to automatically switch from shore power to on-board battery.
A pair of stepper motors actuate the pointing mechanism. A microcontroller keeps track of the location of the stepper motors and reports it to SkySafari through the basic encoder protocol. SkySafari issues GOTO commands to the microcontroller via the same protocol. All projections and translations from steps to sky coordinates are performed by Sky Safari.
TODO: does SkySafari send GoTo commands with the basic protocol?
No screen, no laser pointer, no way to automatically point at objects, calibration needed before every use.
Downside: needs external calibration before use.
A compass and accelerometer are installed on the pointing mechanism. This way, the arrow knows where it is pointed (to a precision of a few degrees) in the local alt-az frame. The arrow can communicate its azm-alt to Sky Safari using the NexStar serial protocol. Conversions from ra-dec to alt-az can be handled with, e.g., astropy.
- SkySafari compatibility with new protocol
- Cycle through scripted celestial objects autonomously
- Slew to follow satellites autonomously
- Cycle through ground-based objects (lon-lat) autonomously
- Read airplane locations from fr24 or adsbexchange
V2, but with a display to show what the arrow is pointing at.
Automatically get time and location from a GPS receiver.
V2, but with a laser to point to interesting objects. The laser is controlled by the microcontroller and there is a safety interlock on the base, requiring the user to be present for use.
To increase precision, the arrow incorporates a camera that looks at the sky and plate-solves. Probably very unnecessary and may make things more complicated if plate-solving is used by day.